Electric blanket control



A. E. RUDAHL ELECTRIC BLANKET CONTROL Filed Jan. 17, 1947 May 30, 1950@vue/miro@ APM/OLD [./QUDAHL @www Patented May 30,' 1950 il TED STATE'SvP'E'JISJT .Arnold .RudahL .MiddlefielL Conn., assignor .toLanders-Frary& Clark, Newlritaim Conn., .acci-poration of ConnecticutApplicationilamuaryfll, 19.47, SerialNo. .722,574

Claims. (01:219-46) The 1 present .invention erelates to ,.electricblankets andv more particularly .to a. temperature control Y systemtherefor uwhich :is f characterized byitsisensitivity totemperatureconditionswvvith- VV1n the blanket itselfiandfalso, ifltl-esirecLftoam-- hient :temperaturesg :which .control systemviswllimpli'lied construction involvinga .minimum Loi .pants .and .thecelimination .of expensive '.equipment, .and .is efcient, .reliable ,and:safe in operation.

It is an object of the present invention dlao-pre- 'videiahontrolcircuit ionelectric Jolanketstwhich wrilkregulategthefamount of:heatgeneratedvwithin fthe blanket to .c-losely...approximate1 the wheatloss therethrough, l such. cirouit.=being responsive to changes intemperature :with-in .the blanket itseifzandJi desiredealso to changesimambient temperatures. iA 'furtlzier object :ofsthezinventionfistoprov-ide a control-system cof @the @type referred fto which .flssafencperatonand which .iseifectiverinV connection :with its lheatregulating functions #for eliminatingithe hhazardssof l I-ire.

Another object of the invention is'to saccomplish vthe loregoingmamed:objectives l'by means of f ascontrnlesystem :which is.of..simplit`1edcon-- struction :requiring Va ammi-mum of parts fand .whienis .notdependent 'fior :its voperation --upon expensive .equipmentorllequipment of the ftype which :can :readily becomeout of vadjustmentand thus require frequent replacementwcrfrepair.

vOther o.bjects fwill be. in ...part .obvious i and :in partpointedout.more. indetailh'ereinafter.

Theinvention accordingly .consistsvin:thefiea tures .of construction,A.combination .zofA elements and arrangement of. .parts .Whichewlhe..exempli fled. in the construction .hereafter .set e forthnnd thescope .of Atheapplication .of iwhich will :be indicated. in the.appended claims.

.Referring .to the drawings- .Elgure lis a 'diagrammaticviewuof .one.emf bodiment. .of .a temperature. controlzsystem constructed inaccordance .miththe invention;` and Fig. 2 is a `diagrammatic view-Lofa=secondem bodiment of the invention. A

Referring particularly to fthe .e embodiment shown'v-inFig.' 1 of the`dravvings,the.reference numeral I0 denotes an electric '.blanket .whichmay be i formed kof f conventional blanketing smateril and whichcontains @therein .-'felectric heating element H,.Which element may 'becomposeld of Ya thin, iiexble resistance uWire AembeddedjinVsuitableinsulating material and ypreferably arrangedin a .plurality ofconvoihitions throughout ,theblanke't soasto providesubstantially even"heating'thereoi". This cons sruction is Welltknownin the art and neednot'Joe -more fully herein.

The reference numeral 'lf2 denotes a control box in `Whichv are 'housedcertain ofthe elements .Whichmake .up the control circuit tobe'described hereinaiter. 'LIn the embodiment shown, these elements.comprise `tvvo thermal relays [3 -and,..,l4 formed with .the .usual'loi-metallic` switch Iarms .L5 and l6 ,-respectiv'ely. Each of 'the" bimetallic switch armsgl `aru'ljis provided with a heater .wire 22! :and-`22, respectively, suitably Wou-nd thereon. .The .thermalrelay L5 fisnormally closed, that .is,. the thermal .switch.arm 'l5 isin-.electrical contact miththestationaryor ajdzustable switch ,arm 7.1.1.through the Contact ,points L8. Y.By the vterm ,normally closed ismeant the conditionnf the thermal relay yat ordinary roomtemperatures...'1`he,therrrla1,relai7 4:47,*,onathe contrary;v isnormally Lopen,.thatis, at ordinary room temperatures 4the thermal switch arm I6 is outof electrical-.:contaot with the ,stationary orfadiustable ,switch armJ9, .thereby separating' the.;contactgpoints 42l). The .construc-.tionpf` the y thermalrfrelay ,i3 ,is suchythat ,it will @pen -.\Mh enthe fbi-metallic strip I5 `'cleconies heatedfas, forjexample, Whenfa.current vis passed through-.the .heater wire 21,. .The;thermal 'relayL4, ,on the otherrfhands iadaptedfto close-,when the-fbifrnetailicl-vrin Liisiheated Suchzas-iwhe current is massed ihrough fthe :heater:wire @22, Such @thermal .1.' relays :ra-re A,Well hknown and arereadily rgavaiiable commercial-lv and, .therefore need :be .f describedmanly :briefly :here- ;.The lin.es.i23ziandi2tane intendemtodei-.10te=.=a conventionalrsource;offelectrical,energy snchias the usualhousehold lighting circuit. Thea-'line 23 z-.isfconnected stoftheiiheatinguelement ill and. alsocto aare'sistance's25Whiclnis'containedwithin the blankettt. iThe;resistaricezsmaymcornprisea resistance i 2 Sgmay comnriseaa resistance .vwire whichfisaarranged in.la plurality.;ofcconvolutions throughout the eblanket, o r .it maycomprise ca serieseoffsmall resistanceslauttons a(:istributed in seriesthroughout theiblanketporiboth. It-.isriinportant only that theresistance 25 shall comprise elements having an electrical conductivitywhich is sensitive to changes in temperature. In the specific embodimentshown, the resistance element 25 is one which decreases in resistancesubstantially proportionately to decreases in its temperature.

The opposite end of the heating element II is connected to the heaterwire 2| which is wound around the bi-metallic switch arm l5, which wirein turn is connected to the stationary switch arm I9 of the thermalrelay I6. The opposite end of the resistance 25 is connected to thestationary switch arm I'I of the thermal relay I5. The bi-metallicswitch arm I of thermal relay I3 is connected to the heater wire 22which, 1n turn, is connected to the line 24. The bi-metallic switch armI6 also is connected to the line 24.

For convenience, the circuit shown in heavy lines running from the line23 through the heater II, thence through the heater wire 2I of thethermal relay I5, and from there through the thermal relay I4 to theline 24 will be referred to hereinafter as the heating circuit. Thecircuit shown in light lines which runs from the line 23 through theresistance 25 and thermal relay I3 to the heater wire 22 of the thermalrelay I4 and from thence to the line 24 will be referred to hereinafteras the feeler circuit.

The operation of the embodiment shown 1n Fig. 1 will be understood fromthe above description taken in connection with the followingexplanation. When the lines 23 and 24 are connected and the apparatus isin the normal condition shown in Fig. 1, the flow of current can onlypass through the feeler circuit inasmuch as the thermal relay I4connected in series with the heating circuit is open. Assuming that theblanket is in a cold condition, the resistance of the feeler resistance25 will be low, thus causing current to pass relatively rapidly throughthe heater wire 22. This supplies heat to the bimetallic switch arm I6which eventually closes the thermal relay I4. Immediately upon thishappening, the heating circuit is closed thereby causing heat to besupplied to the blanket through the heater element II. The passage ofcurrent through the heating circuit, by reason of the heater wire 2|,causes heat to be supplied to the bi-metallic switch arm I5 therebyeventually causing the thermal relay I3 to open, which thus opens thefeeler circuit.

When the feeler circuit is thus opened, current no longer flows throughthe heater wire 22 with the result that heat is no longer supplied tothe bi-metallic switch arm I6 and as this switch arm cools it moves awayfrom the stationary switch arm I9, thereby opening the thermal relay I4.Opening of the thermal relay I4, of course, opens the heating circuit sothat heat is no longer supplied to the blanket I0. Thereupon, no heat isfurnished to the bi-metallic switch arm l5 by the heater wire 2|, whicheventually causes the thermal relay I3 to close, thereby again closingthe feeler circuit and the apparatus is in condition to repeat theoperation as described above.

It will be appreciated that the duration of the heating and non-heatingperiods will be determined by the temperature conditions of the blanketinsofar as this aects the resistance of the feeler resistance 25. Thethermal relays I3 and I4 and the feeler resistance 25 can readily bedesigned and adjusted so as to provide a very sensitive control circuitsuch that only slight 4variations inthe temperature of the blanket I0will occur.

The specific embodiment shown in Fig. 2 is essentially the same as thatshown in Fig. 1 and description of the various elements need not berepeated inasmuch as the same reference numerals have been utilized. Themain difference in this embodiment shown in Fig. 2 lies in the use of anauxiliary resistance 2B in the feeler circuit, which resistance 26 isexternal to the blanket and, as shown in the drawing, may beconveniently located in the control box I2. The resistance 26 is similarin construction to the resistance 25, particularly insofar as the amountof the resistance thereof decreases substantially in proportion todecreases in its temperature.

The eiect of the additional resistance 26 in series with the resistance25 is to make the feeler circuit responsive not only to temperatureswithin the blanket, but also to ambient temperatures. It will be obviousthat as the room becomes colder the length of the heating periods willbe increased, thereby anticipating changes which normaily would takeplace in the blanket I0.

It thus will be seen that there has been provided, in accordance withthe invention, a control circuit for electric blankets which is ofrelatively simple construction eliminating many expensive parts andconstructed of conventional elements which will not readily become outof adjustment. The control circuit is sensitive to temperatures withinthe blanket I0 which not only insures that the desired heatingconditions will be obtained, but thus is additionally effective toovercome the re hazard normally present in electric blankets.

A further safety feature is that any failure of the control or feelercircuit prevents the electric blanket from functioning and, therefore,the blanket cannot be operated unless the controls are in properoperating condition.

As many changes could be made in the above construction and manyapparently widely dierent embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the followingclaims is intended to cover all of the generic and specific features ofthe invention herein described and all statements of the scope of theinvention which, as a matter of language, might be said to falltherebetween.

I claim as my invention:

1. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electrical heating element insaid blanket, a resistance element in said blanket whose resistanceincreases in relationship to increases in its temperature, a firstcircuit for connecting the heating element to a source of electricalenergy, a second circuit for connecting the resistance element to thesource of electrical energy, a normally open thermal relay in said nrstcircuit having a heater wire connected in the second circuit, and anormally closed thermal relay in the second circuit having a heater wireconnected in the rst circuit.

2. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electrical heating element insaid blanket, a resistor in said blanket where it is subject to.temperature conditions within the blanket,

a resistor exterior tthe blanketwliereit is subject toambienttemperaturesreach of said ree7 sistors having-a resistance value-whichincreases infrelationship to increases in its temperature;l a. firstcircuit for connecting the :heating elementfto ajgsource of. electricalenergy, asecond circuit'for connecting the resistors in series. to asource, o f electrical energy, Aa normally.,` openthermal. relay in theiirst circuithaving. a heater Wire connected in the second circuit, anda' normally closed thermal relay. in the secondf circuit? having aheater wire connected in the-irstcircuiu 3. A heat control arrangementfor an electrically heated blanket comprising, in combination, ablanket, an electrical heating element in said blanket, a resistor insaid blanket Whose resistance increases in relationship to increases inits temperature, a rst circuit for connecting the heating element to asource of electrical energy, a second circuit for connecting theresistor to a source of electrical energy, normally open switch means inthe rst circuit adapted to be closed by the iiow of current in thesecond circuit after a time interval dependent on the magnitude of saidcurrent, and normally closed switch means in the second circuit adaptedto be opened by the flow of current in the first circuit.

4. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electrical heating element insaid blanket, a resistance element in said blanket Whose resistanceincreases in relationship to increases in its temperature, a circuit forconnecting the heating element to a source of electrical energy, anormally open relay actuated by the second circuit for closing the firstcircuit after an interval depending upon the amount of current passingthrough the second circuit, and a. normally closed relay actuated aftera predetermined interval of operation by the rst circuit for opening thesecond circuit.

5. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electrical heating element insaid blanket, a resistance element in said blanket Whose resistanceincreases in relationship to increases in its temperature, meansincluding circuits for connecting said elements in parallel to a sourceof electrical energy, normally open means actuated by the ow of currentthrough the circuit connecting the resistance element at time intervalsresponsive to the amount of iiow of current through said resistance forperiodically closing the circuit to the heating element, and normallyclosed means actuated by the iiow of current through the circuitconnecting the heating element at time intervals responsive to theamount of iiow of current through the heating element for periodicallyopening the circuit to the resistance element.

6. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electrical heating element insaid blanket, a resistor in said blanket where it is subject totemperature conditions within the blanket, a resistor exterior to theblanket Where it is subject to ambient temperatures, each of saidresistors having a resistance value which increases with increase in itstemperature, a first circuit for connecting the heating element to a 'fsource of electrical energy, a second circuit for connecting theresistors to a source of electrical energy, normally open switch meansin the first circuit responsive to the amount of iiow of current in thesecond circuit for periodically closeri mgthenrsttcrcuia mdfnormauyfciseu? means iniltli'e' second circuit responsive tbrtheiamountl ofiiow-Sofy current-through the first circuit? forVperiodically?.opening'v the'secondfcircuit'. f 'Il A heatfcont`rolvarrangement? for: an -electrically heated: blanket comprising; in'combination;i a'Y blanket; an'- electrical heating: element inl said".-blanket,- aresistance element invv said? blanket Whose4 resistanceincreasesf inj relationship tain-- creases in its temperature, a secondresistance@ element exteri'ortc therv blanket and subject to ambienttemperatures whose resistance increases in relationship to increases inits temperature; a.. circuit" for connecting: the heating 115i elementto a source of electrical. energyiaecondl circuit for connecting thesaid resistance elements to the source of electrical energy, a normallyopen relay operated after an interval determined by the ow of currentthrough the second circuit for closing the rst circuit, and a normallyclosed relay operated after a predetermined interval by the flow ofcurrent through the iirst circuit for opening the second circuit.

8. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electrical heating element insaid blanket, a resistance element in said blanket whose resistanceincreases in relationship to increases in its temperature, a rst circuitfor connecting the heating element to a source of electrical energy, asecond circuit for connecting the resistance element to a. source ofelectrical energy, thermally responsive means in said rst circuitoperable when heated for closing said circuit, thermally responsivemeans in said second circuit operable when heated for opening saidcircuit, means for heating the first named thermally responsive means inproportion to the amount of current passed through the second circuit,and means for heating the second named thermally responsive means inproportion to the amount of current passed through the rst circuit.

9. A heat control arrangement for an electric blanket comprising, incombination, a blanket, an electrical heating element in said blanket, aresistance element in said blanket whose resistance increasessubstantially directly with increases in its temperature, a normallyopen thermal relay comprising a `bimetallic switch arm and a heater wiretherefor arranged to close the relay when current is passed through theheater Wire, a normally closed thermal relay comprising a .bimetallicswitch arm and a heater wire therefor arranged to open the relay whencurrent is passed through the heater wire, means for connecting theheating element, a switch arm of the second relay and the heater wire ofthe first relay in series to a source of electrical energy, and meansfor connecting the resistance element, a switch arm of the iirst relayand the heater wire of the second relay in series to the source ofelectrical energy.

10. A heat control arrangement for an electrically heated blanketcomprising, in combination, a blanket, an electrical heating element insaid blanket, a resistance element in said blanket whose resistanceincreases in relationship to increases in its temperature, a secondresistance element external to said blanket and subject to ambienttemperatures whose resistance increases in relationship to increases inits temperature, a. normally closed thermally operated relay having abimetallic switch arm and an electrical heater 75 Wire therefor, anormally open thermally operroiatea reiay having bimetauic switch armandr an electrical heater wire therefor, means for connecting theheating element, the heater wire of the rst named relay, and the switcharm of the second named relay nfsere's to a source of electrical energy,and means for connecting the resistance elements, the heater wire of thesecond named relay and thei switch arm of the rst named relay in seriesto the source of electrical energy.

.ARNOLD E. RUDAHL.

REFERENCES CITED The following references are of record in the file ofthis patent:

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